The Life Mage is a great early-game choice, for the Holy Defiance perk. A single point invested there will prevent your creatures from ever being one-shot by attacks.

The first thing you should buy from Bynine is three Nightwing Gargoyle cores (if you do not see them, level up more and they will appear).

Daily Realms are referred to as "a late-game activity" by Licktorr. The early levels are (usually) not too challenging for a new player. There is no cost to enter, no penalty on death, and they give decent rewards. Try it early, but do not be discouraged if you cannot keep a long streak.

The Arena is a late-game thing. You have to win 19 in a row just to get enough points to buy an invitation to replace the one you used.

Potions in Sorcery realms can be good or bad. You may wish to clear all the enemy packs before drinking potions, to avoid a debilitating debuff. Don't skip them though—sometimes they give you Royalty Points.

Once you have Topaz Paragon cores, consider not summoning it. Once you do, you'll also encounter them in the wild, and they generally hurt you far more as enemies than they help you as allies.

It is recommended to invest your early royalty points in resource generation to progress in the game faster

Consider getting a troll-arsonist. Their bomb is immune to enemy counter attacks, enemy defenses, and debuffs on your creature.

For those interested in the different classes and their specific differences:

Calmness: Each rank reduces the amount of damage your creatures take from spells by 3%

Guardian Angel: Each rank grants a 1.5% chance to prevent damage from an incoming attack if that attack would kill your creatures.

Holy Defiance: When your creatures are attacked, and they would take damage greater than 60% of their Maximum Health as damage, reduce that damage to 60% of their Maximum Health. Each Rank reduces this threshold by 1%.

Reinforce: When your creatures are healed, 1% of the amount healed is added to a Barrier for each rank.

Saving Grace: Each rank grants each of your creatures a 2% chance to start battles with Rebirth